Presynaptic nerve terminals (presynaptosomes) will be isolated from the electric organ of Torpedo marmorata. The membranes of this preparation will be subfractionated to obtain discrete membrane fractions which differ in protein composition. Antibodies will be prepared to the major proteins of each subfraction. Immunoelectromicroscopy and chemical labelling techniques will be used to identify the location of these proteins within the nerve terminal. Parallel experiments will investigate the effects of depolarization and neurotransmitter release on the structure and localization of these membrane proteins.